Make sure you save your SHSH blobs using Tiny Umbrella ASAP! As per the Devs, the exploit is patched in 4.3 (soon to be released), and Apple will stop signing 4.2.1 around the same time, at which point you would be out of luck until a 4.3 exploit is released.

- a supported device (see above)
- the device should run iOS 4.2.1. Please check on the device in the Settings -> General -> About page.
If your device is running an older version, please upgrade iOS first using iTunes.
*** If you want to SIM Unlock, preserve your baseband using TinyUmbrella ¬***
- at least MacOSX 10.5

> Notes (checks this also !)

- if your device is jailbroken with iPhone Dev Team's Monte, please restore to fresh 4.2.1. first
- if Cydia doesn't show up after Loader, you may need to reboot the device
- this version of greenpois0n doesn't include a patched activation system. You'll need to activate your device using iTunes
- WE DO NOT SUPPORT PIRACY !

> Instructions

1. plug the device to your computer using the USB cable
2. quit iTunes if it shows up
3. start greenpois0n.app
4. follow instructions
5. the device will boot a 1st time with verbose text on screen. This operation will install the jailbreak on the device.
6. the device will reboot normally
7. start the Loader application (green icon on the SpringBoard), and follow instructions to install Cydia